The present invention relates to a heating cooker for heat-cooking foods by using steam.
Heretofore, as a heating cooker for heat-cooking an object to be cooked such as food by using steam, there is a heating cooker with a steam generator disclosed in JP 4-123790 A (reference 1). The heating cooker with a steam generator includes a heating chamber, an induction heating coil, a tank, a water reservoir and an opening/closing valve. Then, with vaporization water fed to the water reservoir, the opening/closing valve is opened to fill the tank with water, and the induction heating coil is turned on with an alternating current so that the tank is heated by an alternating magnetic field generated in the coil to generate steam. The generated steam is sent into the heating chamber, thus allowing the heat cooking to be carried out.
However, the heating cooker with a steam generator disclosed in the above reference 1 involves manpower for supply of water to the water reservoir. The opening/closing valve is to be operated also by hand. Due to this, even if the tank is emptied, the heating chamber is continued to be heated, accompanied by a risk of overheating damage, catching fire or the like. Further, since the tank is fixed, there is an inconvenience that the water supply has to be done by using a water container for water-carrying use.
Accordingly, in order to solve the risk and the inconvenience, it is conceivable to provide an auxiliary tank which has a bottom portion communicated with a bottom portion of the fixed tank while having an upper end opened, and in which a water level sensor is set up, the water level sensor functioning to detect a water level within the tank. In this case, since the water in the auxiliary tank goes up until its water level becomes flush with that of the fixed tank, the water level in the fixed tank can be detected by detecting the water level in the auxiliary tank by means of the water level sensor. This water level detection method is often used because it requires no setting of the water level sensor on the fixed tank side, which is to be directly heated, so that the water level in the fixed tank can be detected conveniently.
In the case where the water level in the tank for generating steam is detected by the water level sensor of the auxiliary tank, unfortunately, there is a problem as shown below. That is, since the fixed tank is closed, continued heating of the heating chamber causes the generated steam to become increasingly filled in the tank and the heating chamber, which in turn causes pressures in the tank and the heating chamber to increase due to the difference in volume between water and steam, the latter being larger. Then, the water surface in the tank is pressed by the increased pressure, causing the water in the auxiliary tank to be forced up with its water level no longer lowered. Meanwhile, the water in the fixed tank, which evaporates, continues to decrease.
Therefore, the water level in the fixed tank and the water level in the auxiliary tank differs from each other, giving rise to cases in which the auxiliary tank is not emptied even when the fixed tank is substantially emptied, so that the water level sensor outputs a normal value. In this case, because the water level sensor outputs a normal value, the fixed tank is not supplied with water, accompanied by a risk of heating without water.